Hard chrome is not the be all, end all. Because it is a coating it can peel and flake under various conditions. Any moisture will cause rust and the chrome bubbles and peels. Likewise, heat can cause it to peel and flake. If there happens to be a flaw in the plating, trouble will start right there.

Hard chrome is not necessary for a nodular iron rocker. The fact that the rockers and shafts are dissimilar metals (iron and steel) minimizes the chances of problems arising as long as they're well lubed.

FWIW, when the factory put iron rockers on various motors they used a plain ol' shaft - nothing fancy. And aftermarket iron rockers worked fine on stock shafts - the only problem with stockers being that they were thin walled and prone to being squeezed oval when tightening the hold downs, making rocker removal a [censored]! Hemis were the only motors with iron rockers that got bushings.

Buy a quality steel shaft and you'll do just fine.